Numerous countries throughout the world—particularly in desert and equatorial regions—are characterized by an arid climate and sandy soils. These sandy soils have low water retention capability and require large amounts of water for irrigation purposes. Due to the arid climate and lack of fresh water resources, the water that is used for irrigation is produced mainly through desalination of sea water which is an expensive process. Materials with good water retention capabilities could be very useful in reducing the water consumed for irrigation purposes. Additionally, they can also be used to reduce erosion and water run-off in other regions of the world.
Superabsorbent polymers such as Polyacrylamides (PAM) and other acrylic based polymers have been extensively investigated as a candidate for an efficient water absorbent for irrigation purposes1-5. The slow absorption of water, slow biodegradation and high cost of polyacrylamides are the challenges faced which limits the wider use of this material in agriculture6. Additionally, even though polyacrylamides are not toxic, traces of toxic unpolymerized arcylamide can be present in commercially available polyacrylamides which makes it unsafe for use in agriculture7. Natural materials such as wood chips and saw dust can be applied as soil amendments to increase the water storage capacity of sandy soils, however, water retention in wood is low8. Cheap and biodegradable water absorbing polymers could be an answer to address the irrigation challenges in arid climates.
Cellulose is the most abundant biopolymer which can be extracted inexpensively from plants, some animals, fungi, algae and bacteria9,10. More importantly, it is abundantly present in the form of paper waste. Cellulose is known for its hydrophilicity, chirality, broad modifying capacity and its formation of versatile semicrystalline fiber morphologies11. The biodegradable nature of this inexhaustible biopolymer has encouraged scientists to develop cellulose based composite materials which can be used as eco-friendly substitutes to existing non-biodegradable fossil fuel based counterparts. Modifying native cellulose can change its structure and crystallinity which essentially determine its physical properties, accessibility to chemical modification, swelling and adsorption phenomenon10. Polysaccharide based superabsorbent materials have also been explored. They are produced mainly through graft polymerization of suitable vinyl monomer(s) on polysaccharide in the presence of a cross-linker or direct cross-linking of polysaccharides12,13.